Electrical motor and generator



May 31, 1932. c. H. THORDARSON ELECTRICAL MOTOR AND GENERATOR Filed May4, 1926 2 Sheets-Sheet 1 May 31, 1932.

C. H. THORDARSON ELECTRICAL MOTOR AND GENERATOR Filed May 4, 1926 2Sheets-Sheet 2 Patented May 31, 1932 UNITED STATES PATENT OFFICE CHESTERH. THORDARSON, OF CHICAGO, ILLINOIS, ASSIGNOR TO THORDARSON ELEC- TRIOMANUFACTURING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOISELECTRICAL MOTOR AND GENERATOR Application filed May 4,

This invention relates to improvements in electrical motors orgenerators, and is more particularly adapted for high voltage directcurrent machines.

The invention is chiefly characterized by providing a metallic shieldbetween the periphery of the armature and the pole faces and maintainingthe shield at a potential difference intermediate that of the terminalsof the machine.

Although broadly considered the invention may be practiced bysub-dividing the electrostatic field between the armature and the polepieces and maintaining at least half of the sub-divided fieldsubstantially uniform, this latter sub-division is preferably effectedby interposing an electrostatic shield between the armature and polepieces, which shield ispreferably maintained at a potential differencehaving a value intermediate that of the terminals of the machine. Themain objects are to decrease the insulation losses ofthe armature; toreduce the leakage current losses at high voltages and to reduce thesurface creepage losses; to maintain a low resistance to the magneticflux and to reduce hysteresis and eddy current losses; to providea-machine adapted for higher voltages than heretofore attained; and toreduce the length of the total air gap.

An illustrative embodiment of this invenion is shown in the accompanyingdrawings, in which Figure 1 is a: View in partial cross section of abipolar machine.

Fig; 2 is aplan view of Figure 1.

Fig. 3 is a diagram'of one form of electrical connections.

Fig.- 4 represents a barrel type ring-wound armature.

In electric machines in general it is highly desirable that the air gapbetween the armature andpole-pieces be reduced to a minimumr However,the dimensions of the gap are usually confined to certain minimumdimensions determined by the working voltage of the machine and thedesired clearance. In'the case ofhigh voltage machines the clearance isordinarily" greater than in low voltage machinesbecause of the greatertendency to 1926. Serial No. 106,696.

disruptive discharges between the armature conductors and thepole-pieces proper which are usually connected to the frame andgrounded. In accordance with the present invention it is proposed toachieve greater safety against such disruptive discharges in highvola-ge machines by sub-dividing the gap between the armature proper andthe polepieces into two parts which are separated by an electricalconductive member or shield capable of being maintained at a fixedpotential difference, which is preferably of a value less than themaximum operating potential of the machine. As a result of thissub-division and as a result of the constant potential difference whichis maintained between the armature proper and the pole-pieces or framethe insulation of the armature conductors is subjected to asubstantially constant or at least a uniform electro-static fieldthroughout the entire periphery of the armature. Furthermore theelectrostatic strains which are set up in the insulation betweensuccessive armature portions are provided with a parallel path to theshield. Consequently at any pointin the periphery of the armature themaximum strain to which the armature insulation is subjected is thatdetermined by the potential difierence of the shield.

Illustrating one particular manner of carrying out the features of theinvention there is shown in the drawingsan armature 1 rotatably mountedin the pedestal bearings 2 and 3 which are supported by the base 4. Thefield frame 5 is mounted on the base a, intermediate the bearings and isprovided with squared hubs 6, in which the pole pieces 7 are mounted.The field coils 8 are mounted on the outwardly extending ends of thepole pieces, and the inner ends or faces 9 of the poles are made concaveto conform to the surface of the armature 1 in the usual manner.

The metallic shield 10 comprises a cylindrical tube preferably ofamaterial having preferably electrical and magnetic characteristics of ametal such as silica iron. The shield 10 is mounted on the innersurfaces of the pole faces 9 and insulated therefrom by means of a layer11 of such material as mica. The mica tube 11 extends laterallybeyondthe poles to lengthen the creepage path from the armature to theframe of the machine.

The shield 10 is held at a potential inter mediate the potentialdifference of the machine, and the air gap between the shield and theperiphery of the armature may thereby be considerably shortened over theair gap which would be required for the full voltage between the poleand the armature.

As is well known the strains set up in a dielectric as well as thedisplacement currents and heating efiects therein increase as thevoltage difi'erences applied to the dielectric increase. In the usualtype of machine where the frame and pole-pieces areconnected to groundor zero potential the potential difference between the pole-pieces andthe peripheral insulation of the armature corresponds to the maximumpotential encountered in the machine proper. However, when the abovedescribed shield is interposed between the pole-pieces and the peripheryof the armature and maintained at a constant voltage which is lower thanthe maximum voltage of the machine there is a tendency to disruptivebreak-down between the armature insulation and the pole-piece. Forexample, if the machine is a generator, designed to generate 5000 voltsand the shield 10 is maintained at a potential difierence of 2500 voltsthe maximum strain on the armature insulation corresponds to a potentialgradient of 2500 volts, whereas without the shield the armatureinsulation may be subjected to potentials as high as 5000 volts.

The machine shown is bi-polar and has a barrel type ring-wound armature,and may be used either as a generator or a motor. An illustrative formof electrical connections is diagrammatically shown, in which the endsof the armature coils 12 are connected to adjacent ones of thecommutator bars 13. The bars are connected by means of the brushes l4and 15 to the main lines 16 and 17 respec tively. The brushes Contactwith segments half way between poles and the current divides and flowsthrough the series of coils on either side to the opposite brush.Preferably, the low potential brush 15 is grounded to the frame of themachine. The shield 10 is held at an intermediate potential by aconnection to a third brush 18 which contacts with a commutator bar halfway beween the main brushes 14; and 15.

The commutator bands 19, which are pro vided to hold the coils 12against the centrifugal force, are in close relation with the coilscarrying the maximum potential and may be considered as being at thehighest potential with regard to possible leakages.

By reducing the voltage drop to the bands or the armature surface, asdescribed, higher voltages may be impressed before the air gapresistance is broken down.

Although but one specific embodiment of this invention has been hereinshown and described, it will be understood that numerous details of theconstruction shown may be altered or omitted without departing from thespirit of this invention as defined by the following claims. Thus anywell known means may be employed for controlling the potential gradientbetween the periphery of the armature and the pole-pieces.

I claim:

1. In an electrical machine of the class described, a rotating armature,fixed field poles about the periphery of the armature, a cylindricalmetallic shield surrounding the armature and insulated from the fieldpoles, and means for maintaining the shield at a predeterminedpotential.

2. In an electrical machine of the class described, a rotating armature,fixed field poles about the periphery of the armature, and a metallicshield mounted on and insulated from the inner faces of the poles, saidshield surrounding the armature and spaced therefrom, and means formaintaining the shield at a predetermined potential.

3. In an electrical machine of the class described, a rotating armaturehaving tenninals at a potential difference, field poles fixed about theperiphery of the armature, a cylindrical metallic shield mounted on theinner faces of the poles to surround the armature, said shield beinginsulated from said poles and spaced from the periphery of the armature,one of said terminals being grounded to the machine frame, and means formaintaining the shield at a potential intermediate the potentials ofsaid terminals.

4. In an electrical machine of the character described, an armature, afield pole for said armature, and means interposed between said armatureand said pole for controlling the maximum electro-static strain on thearmature insulation, said last mentioned means adapted to be maintainedat a potential lower than the maximumworkin g potential difi'erence ofthe machine.

5. In an electrical machine of the character described, an armature,coils mounted on said armature and insulated therefrom, field magnetsand separate means for controlling the potential difference between theperiphery of the armature and the field poles.

6. In an electrical machine of the character described, means forreducing insulation losses comprising a conductive shield surroundingthe armature, and means for maintaining said shield at a fixed potentialdifference, said potential difference being less than the maximumworking potential of the machine.

7. In an' electrical machine of the character described, an armature, aplurality of field poles for said armature, and a conductive shieldextending before all said field poles but insulated therefrom, saidshield being spaced from said armature, and means for maintaining theshield at a potential difference intermediate the minimum and maximumworking potentials of the machine.

8. In an electrical machine of the character described, a rotatingarmature, a plurality of field poles surrounding the armature, aconductive shield, said shield being mounted in spaced relation bothwith respect to the armature and with respect to the field poles, andmeans for maintaining said shield at a potential difierence less thanthe maximum working potential of the machine.

9. An electrical machine according to claim 8 in which the shield is inthe form of a cylinder, and is freely spaced from the armature, but isseparated from the field poles by a layer of solid insulation.

10. A machine according to claim 8 in which the shield is insulatinglymounted on the pole-pieces.

11. In a machine of the character described, a rotating armature, acommutator for said armature, a conductive shield surrounding saidarmature, a pair of brushes connected to said commutator, another brushfor said commutator intermediate the said pair of brushes, and aconnection from said other brush to said shield.

12. An electrical machine according to claim 11 in which one of thebrushes of said pair is grounded.

13. A machine according to claim 11 in which the said other brush ismidway between the pair of brushes.

14:. A machine according to claim 11 in which the shield is in the formof a metallic cylinder freely spaced from the armature and insulatedfrom the pole-pieces.

15. In an electrical machine of the character described the method ofreducing armature insulation losses, which comprises subjecting thearmature insulation to the action of an equipotential surface in spacedrelation to the armature, the potential for said surface beingintermediate the zero and maximum Working potentials of the machine.

16. The method according to claim 15 wherein the potential difference ofthe shield is one-half the maximum potential of the machine.

17. In an electrical machine of the character described, means forreducing armature insulation losses including a member in closeproximity to the armature and insulated therefrom, and means forapplying to said member a constant potential intermediate that of themachine terminals.

18. In an electrical machine of the character described, means forreducing insulation losses, comprising a conductive shield surroundingthe armature, and means for maintaining said shield at a fixed potentialbut less than the maximum working potential of the machine.

19. In an electrical machine of the character described, means forreducing insulation losses including a conducting member mounted inproximity to the armature but freely spaced therefrom, and means forapplying to said member a constant potential intermediate the potentialof the machine terminals.

20. In an electrical machine of the character described the combinationof an armature, an equipotential surface in spaced relation to saidarmature and surrounding the same, and means for maintaining saidsurface at a potential difference lower than the maximum potential ofthe machine.

Signed at Chicago this 30th day of April,

CHESTER H. THORDARSON.

